A dozen Democrats in the U.S. Senate are seeking answers from the Department of Education over its decision last week to delay the effective date of the gainful-employment rule until July 1.

In a letter, the senators, led by Richard J. Durbin of Illinois, Patty Murray of Washington, and Elizabeth A. Warren of Massachusetts, called on Betsy DeVos, the education secretary, to explain the decision. Several senators also asked the department’s inspector general, Kathleen Tighe, to investigate the choice.

“The gainful-employment rule is a critical protection for both students and taxpayers,” the letter says. “This delay needlessly stalls important protections for students and taxpayers, and creates more uncertainty for schools.”

The rule, crafted under the Obama administration, is intended to judge career-oriented programs based on the student-loan debt of their graduates in relation to the graduates’ earnings. “Implementation of this rule is an important part of your responsibility as secretary to protect students and appropriately oversee taxpayer dollars,” the letter says.

Lynn Mahaffie, acting assistant secretary for postsecondary education, said last week that the decision to delay the rule was intended “to allow the department to further review the GE regulations and their implementation.”

The senators asked Ms. DeVos for a “prompt response” to their questions, but if recent history is an indicator, they may be waiting a while. In a letter to Ms. DeVos in late February, senators requested clarification of reports of a higher-education task force to be led by Jerry Falwell Jr., president of Liberty University. The senators wrote that they wanted a response “no later than” March 9, but as of this writing, they had not yet received an answer.